Thermal and Structural Transient Modelling of Plasma Process for Silicon Carbide

Abstract

[EN] Silicon Carbide (SiC) is a lightweight material which is used in the fabrication of large space mirrors, of more than 500 millimetres diameter, and with a target of achieving an optical surface thickness of less than 1.5 millimetres. SiC is used in space optic applications, such as Earth observation cameras and space satellites, not only because of its lightweight properties, but also because of its mechanical properties like high stiffness and thermal properties like low thermal expansion. SiC has been one of the most used materials for space application mirrors since the nineties when the development of the processes and equipment was produced. Plasma process is the last of the machining processes during the manufacturing phase, after grinding and polishing. Throughout this project a support for this manufacturing process is done based on Finite Element Analysis. This is done by developing thermal and structural transient model with commercial code software (Abaqus). For this purpose, the different parameters which affect during plasma process heat transfer modelling results are analysed taking into consideration static test cases, which experimental data is supplied. 3D models are developed to represent plasma process. After the study of the plasma process static test cases, welding thermal and structural model is created and compared with literature available, in order to model a similar process. A plug-in available for Abaqus, Abaqus Welding Interface, is used for the generation of welding simulations. Comparison with literature simulation results is not completely satisfactory, and for this reason just general trends are indicated in the case of a dynamic plasma heat source. Recommendations for modelling plasma process are made, including: 1) heat input application as surface heat flux or volume target temperature of elements affected by heat source if known can be implemented, 2) a further study of the film coefficient applied to the model according to the experiment should be done, as this have strong influence in the cooling after plasma process, and 3) radiation losses can be neglected since its effect is minimum and does not any relevant effect over temperatures in the plate, and consequently in residual stress appearing